1. Field of the Invention
This invention relates to apparatus for winding webs to form supply rolls under a substantially constant web tension comprising a winding shaft, which is rotatably mounted in a machine frame and driven by an electric motor, a rocker, which is pivoted to the machine frame and has mutually opposite, freely protruding arms, which are equal in length and at their ends carry freely rotatably mounted dancer rollers, and means for detecting a deflection of the rocker resulting in a displacement of said dancer rollers from a normal position, in which they are horizontally aligned.
2. Description of the Prior Art
Published German Application No. 15 74 466 discloses an apparatus which is of that kind and serves for winding a single web to form a supply roll. That apparatus comprises deflecting rollers, which are rotatably mounted at fixed locations in the machine frame, and a rocker, which causes the web to form a loop between said deflecting rollers and comprises arms which differ in length and carry dancer rollers. In that case a weight is required to compensate only the torque which is equal to the difference between the mutually opposing torques which are due to the tension of the web acting on the arms. That compensating weight is carried by a lever that is secured to a shaft to which the rocker is nonrotatably connected. In that known apparatus if is no longer necessary to apply large opposing torques to pairs of one-armed levers, each pair of which carries only a single dancer roller extending between said levers and subjected to a force that equals twice the force which is due to the tension of the web.
When it is desired to form supply rolls by winding webs which travel in juxtaposition and are made by a two-up processing, such as webs composed of tear-off bags, it is usually required to provide two winders, which are provided with respective web tension controllers, each of which controls the drive means of the associated winder so that the webs are wound up under substantially the same web tension. But the provision of two winders provided with respective web tension controllers involves a relatively high expenditure, which increases the cost of the plant.